介词后可以跟句子吗?

介词后当然可以跟句子，即从句；
例：They are talking about when they will visit the Great Wall.

祝你进步！

可以加从句啊

i have no idea of when they will come.
你看看

可以加从句

I want to introduce you to Mr Green ,which is the most famous professor of our school.

可以的，很常见，你要多留意哟！

可以